Thermally responsive actuator



Patented July 4-, 1961 2,990,716 RESPONSIVE ACTUATOR North Easton, Mass,assignor to Texas Incorporated, Dallas, Tex., a corporation Thisinvention relates to thermally responsive actuators and to control meansincorporating such actuators.

An object of this invention is to provide a new and improved thermallyresponsive actuator having improved operating characteristics.

A further object of the invention is the provision of such an actuatorwhich is simple in construction, dependable in operation and capable ofbeing easily and expeditiously manufactured.

A further object of the invention is the provision of such an actuatorwhich takes advantage of volumetric expansion and contraction of athermally responsive medium.

Other objects all be in part obvious and in part pointed outhereinafter.

The invention accordingly comprises the elements and combinations ofelements, features of construction, and arrangements of parts which willbe exemplified in the structures hereinafter described, and the scope ofthe application of which will be indicated in the following claims.

In the accompanying drawings, in which one of the various possibleembodiments of the invention is illustrated:

FIG. 1 is an elevational view in section of a thermally responsiveactuator according to one embodiment of the invention, the actuatorbeing shown in operative relationship with an electrical switch;

FIG. 2 is a fragmentary elevational view in section taken along line 2-2in FIG. 1; and

FIGS. 3 and 4 are fragmentary elevational views in section of portionsof actuators according to two other respective embodiments of theinvention.

Referring to FIG. 1, a thermally responsive actuator according to afirst embodiment of the invention is shown as being generally designatedby the reference numeral and in operative relationship with anelectrical switch generally indicated by the reference numeral 12.Thermally responsive actuator 10 includes a tubular member 14 having aclosed end 16 to provide a cylinder 18 for the reception of a plunger orpiston 20. Piston 20 is disposed in interfitting, slidable engagementwith the internal wall presented by cylinder 18. Within thevariablevolume chamber provided by cylinder 18 with piston 20 disposedtherein is a thermally responsive, solid material 22. By solid materialas used herein there is intended material contra-distinguished fromliquid or gaseous material.

Piston 20 has a piston rod 24 which extends through an interfittingaperture 26 provided by an annular member 28 for guiding the piston rodin its vertical movement as viewed in FIG. 1. The end 30 of tubularmember is opposite end 16 is turned in, as shown, to retain annularmember 28 in fixed position relative to the tube. A compression spring32 is disposed about a portion of piston rod 24, has one end bearingagainst piston 20 and its opposite end bearing against annular member 28thereby to bias piston 20 toward and against thermally responsive, solidmaterial 22 and to bias member 28 against the turned-in end of tubularmember 14.

Thermally responsive, solid material 22 is suiiiciently deformableentirely to fill the chamber in which it is disposed under the pressureexerted thereagainst by piston 20 due to the relatively strong forceexerted against piston 20 by spring 32. Material 22 has a highercoefficient of thermal expansion than the material of cylinder 1% and,upon heating of this material, the latter expands volumetrically againstpiston Thermally responsive material 22 is sufiiciently resistant todeformation to prevent the entry thereof between piston 20 and theadjacent portion of the internal wall of cylinder 18. in this regard, solong as the thermally responsive material is sufficiently resistant todeformation, the inner diameter of cylinder 18 and the outside diameterof piston 20 can often be formed with common (i.e. comparatively wide)manufacturing tolerances without the possibility of such entry of thethermally responsive material.

One of the important features of the actuator according to the inventionis that advantage is taken of the volumetric rather than merely thelineal expansion and contraction of the thermally responsive material22. Volumetric expansion of the thermally responsive material isprevented in all directions except against the piston 2i) with theresult that this volumetric expansion is confined to the linealdirection against piston 20. Conversely, of course, volumetriccontraction of the thermally responsive material is confined to thelineal direction away from piston 2%. It will be clear that for a giventemperature change the amount of movement of piston 20 due to thevolumetric expansion and contraction in opposite lineal directions ofthe thermally responsive material 22 is significantly greater than thatafforded by the lineal expansion and contraction in opposite linealdirections of the same or corresponding materials. Accordingly, it willbe apparent that not only must thermally responsive material 22 besufficiently deformable entirely to fill the chamber in cylinder 18under the pressure exerted by spring 32 through piston 20 against thethermally responsive material, but the latter must also be sufficientlydeformable to expand and contract volumetrically in the opposite linealdirections against and away from the piston 20 upon correspondingtemperature changes thereof. To the extent it is true that the less theplastic deformation that takes place, the longer will be the useful lifeof the thermally responsive material; it is preferable that thismaterial be as elastically deformable (as opposed to plasticallydeformable) as is compatible with the other parameters thereof. it willbe clear that piston 20, being resiliently biased by spring 32 againstthermally responsive material 22, follows and remains in engagement withthe latter during contraction thereof when its temperature is lowered.

.An example of a thermally responsive material having the requisitedeformation characteristics as described above is a silicone rubber soldunder the trademark Silastic 152, which is a trademark of Dow CorningCorporation for a silicon rubber material having characteristics whichprovide high tensile strength, elongation and tear resistance withoutlong oven cure, and which has very good clielectrical properties and lowwater absorption. (Tubular member 14 may be formed, for ex ample, ofstainless steel.) Materials such as Silastic 152 which have acomparatively high coefficient of thermal expansion are particularlyadvantageous in that this high expansion characteristic, taken incombination with the feature of volumetric expansion and contraction inopposite lineal directions, results in a relatively large movement ofpiston 20 per unit change in temperature of the thermally responsivematerial.

Among other advantages of the actuator according to the invention, it isto be noted that no sealing problem between the outer periphery of thecylinder and the inner 3. periphery of the adjacent portion of the innercylinder wall is necessary, because the thermally responsive material issufliciently resistant to deformation to prevent the entry thereofbetween the piston and cylinder wall.

The thermally responsive material 22 according to the embodiment shownin FIG. 1 is in the form of a single, integral piece. This being thecase, it is apparent that handling of the component parts of theactuator and assembly thereof is a very simple matter. Also, advantagecan be taken of thermally responsive material 22 which is practicallyincompressible, as opposed to spongy, so that a positive movement of thepiston 20 occurs upon a temperature rise of the actuator asdistinguished from an amount of movement of the piston dependent uponthe magnitude of the yieldable load against which it moves. It will beclear that such factors as variations in atmospheric or otherwisecircumambient pressure will have practically no effect on thecalibration of the actuator so long as the thermally responsive materialis practically incompressible. Of course, the thermally responsivematerial as well as the remaining parts of the actuator must be stableunder the conditions of temperature, etc. to which the actuator is to besubjected.

The thermally responsive actuator of this invention is useful for anumber of purposes including signaling and controlling or operating asecond mechanism, all of these in response to temperature change. By wayof example, the thermally responsive actuator could be utilized tooperate a second mechanism in the form of a valve for a hydraulic orpneumatic system in a manner well known to those skilled in the art. Inthe arrangement shown in FIGS. 1 and 2, an electrical switch 12 is shownin operative relation with the actuator 10, this to provide a signalingfunction or a controlling function, depending upon appropriateelectrical connection of the switch 12.

Electrical switch 12 includes a hollow casing member 34 formed of one ofthe conventional, moldable, electrically insulating materials andsecured to and closed by a supporting plate 36 with means such as screws38, 38. Tubular member 14 is secured at its upper end to supportingplate 36 such as by brazing at 39. Disposed within casing member 34 area pair of electrically conducting, L-sh-aped, contact-carrying arms 40and 42, respectively. Contact-carrying arm 40 is supported at one levelby means of a rivet 44 having a flange 46 hearing against the adjacentsurface of contact-carrying arm 40. The shank of rivet 44 extendsthrough successive aligned apertures in contact-carrying arm 40, a boss48 integral with casing member 34, and an electrical terminal 50. In asimilar manner, contact-carrying arm 42 is supported at a second levelby means of a rivet 54 having a flange 52 at one end. The shank of rivet54 extends in succession through aligned apertures in contact-carryingarm 42, boss 48, and an electrical terminal 56. Each of rivets 44 and 54is headed over at the end adjacent the terminals t) and 56 thereby tosecure the parts through which it extends in the relationship shown inFIGS. 1 and 2.

Contactcarrying arm 40 supports an electrical contact 58 in co-operatingrelationship with an electrical contact 60 carried by member 42. Each ofcontact-carrying members 40 and 42 is formed of a resilient,electrically conductive spring material such as beryllium-copper orPhosphor-bronze. Each of contact-carrying members 40 and 42 isinherently and resiliently biased in the direction away from the other.The outer end of piston rod 24 is capped with a member 62 formed ofsuitable electrical insulating material (such as ceramic), the latterbeing disposed in engagement with a dimpled portion 64 ofcontact-carrying member 40 and electrically insulating piston rod 24from contact-carrying member 48.

It will be apparent that with the parts in the full-line positions shownin FIG. 1 at which contacts 58 and 68 are separated from each other,heating of thermally responsive material 22, resulting in upwardmovement of piston 20, moves cap 62 against contact-carrying arm 49thereby to move contact 58 toward and ultimately into engagement withelectrical contact 60. Suflicient subsequent cooling of thermallyresponsive material 22 results, of course, in opening of contacts 58 and60. An adjustment screw 66 is provided for calibration purposes. Screw66 includes a shank 68 threadedly engaged with casing member 34 andcarries a projection 70 formed of a ceramic or other electricalinsulating material. It will be apparent that rotation of adjustmentscrew 66 in opposite directions is eifecu've to adjust the position ofcontact-carrying member 42 within the casing 34 and therebycorrespondingly to adjust the respective temperatures of thermallyresponsive material 22 at which contacts 58 and 60 close and open.

Actuator 10 is readily and easily assembled simply by successivelyinserting thermally responsive material 22 (in this case as a unitarypiece), piston 20, compression spring 32 and annular member 28 intotubular member 14 from the upper end thereof as viewed in FIG. 1 andthen turning in the upper end of the latter to retain the parts asshown.

Although thermally responsive material 22 is described above as being inthe form of a single unitary piece, it, as well as that of each of theremaining embodiments to be described, can be in the form of a pluralityof pieces and can even be particulate so long as the pieces or particlesare sufliciently large as to be incapable of entry between anyrelatively movable surfaces adjacent the thermally responsive material.Also, the thermally responsive material may include particles of amaterial (such, for example, as aluminum in many cases) which has ahigher thermal conductivity than the remainder of the thermallyresponsive material, this to increase the thermal conductivity of thelatter as a whole.

Referring to FIG. 3, a second embodiment of the actuator according tothe invention is shown. According to this embodiment, acylinder-providing, tubular member 72 has its end opposite the pistonclosed by a plug 74, the latter being provided with a step 75 about itsperiphery to interfit with the respective end of tubular member 72. Plug74 is fixedly secured to the end of tubular member 72 by any suitablemeans such as brazing. Integral with or otherwise fixedly carried byplug 74 is a member in the form of a shank 76 composed, as is plug 74,of material having a higher thermal conductivity than that of thermallyresponsive material 78 through and against which the shank extends ingood heat-transfer relation. Piston 80, piston rod 82 and compressionspring 84, as well as the remaining parts of the actuator embodiment ofFIG. 3, are or may be identical with their respective counterparts inthe embodiment as shown in FIG. 1 except as particularly pointed outhereinafter. According to the embodiment shown in FIG. 3, piston isprovided with a bore 86 for the reception of the distal end of shank'76. It will be apparent that the tolerances of the outside diameter ofshank 76 and the diameter of the internal wall of bore 86 provided bypiston 80 need be no smaller than substantially that described abovewith respect to the outside diameter of the piston and the adjacentportion of the cylinder wall.

With heating of thermally responsive material 78 the latter expandsvolumetrically in the lineal direction against piston 80, thus movingthe piston upwardly as viewed in FIG. 3 and along the respectivelyadjacent portions of the internal wall of the cylinder provided bytubular member 72 and of the distal end of shank 76; the converse beingtrue upon cooling of thermally responsive material 78.

An advantage of the actuator embodiment shown in FIG. 3 is thatthermally responsive material 78 as a whole will be more quicklyresponsive to a change in temperature of the ambient of the actuator dueto the more rapid conduction of heat along shank 76 to and from theinterior of thermally responsive material 78. Examples of the materialof which shank 76 and plug 74 may be formed are copper or aluminum.

The embodiment as shown in FIG. 3 incorporates a modification which, aswill become apparent as this description proceeds, can be incorporatedas well into the respective embodiments as shown in FIGS. 1 and 4.According to this modification piston 80 provides a shoulder 85co-operable with a shoulder 87 provided in tubular member 72. Dependingupon such factors as the minimum temperature to which the thermallyresponsive material will be subjected, shoulder 87 will act as a stoplimiting the extent of retraction of piston 80 upon engagement ofshoulder 85 with shoulder 87 during contraction of the thermallyresponsive material as its temperature drops. That is, if thetemperature of thermally responsive material 78 continues to drop pastthe point at which shoulder 85 comes into engagement with shoulder 87,further retraction of piston 80 is prevented as contraction of thethermally responsive material continues. Conversely, and with thermallyresponsive material 78 at such a temperature lower than that at whichshoulders 85 and 87 come into engagement during a temperature drop,piston 80 will not begin to move until the temperature of the thermallyresponsive material rises to a particular value. An advantage of thismodification is that of less total movement of the piston for a givenchange in temperature of the thermally responsive material in anenvironment where, for example, space is limited. It will be noted thatwhether or not the actuator is provided with such stop means limitingthe extent of retraction of the piston, the thermally responsivematerial must be sufficiently deformable entirely to fill the chamber inwhich it is disposed at least at a particular minimum temperaturethereof.

The actuator according to the embodiment of FIG. 3 can be assembled inthe manner described with respect to the embodiment of FIG. 1 exceptthat plug 74- would first be secured in the position shown beforeinsertion of the remaining parts into tubular member 72; or,alternatively, said remaining parts could be inserted from the lower endof tubular member 72 after which plug 74 with shank 76 would bepositioned and the plug secured to the end of tube 72.

As with the embodiment shown in FIG. 3, the respective parts of theembodiment of FIG. 4 are or may be identical with their counterparts inthe embodiment of FIG. 1 except as particularly pointed out herein.Piston 88, piston rod 90 and compression spring 92 are shown in FIG. 4as being substantially identical with their counterpart in theembodiment of FIG. 1. The cylinder-providing, tubular member 94 of thisembodiment, however, includes an increased-diameter portion generallyindicated by the reference numeral 96. Portion 96, in section as shownin FIG. 4, is provided in the form of a smooth curve to accommodatedeformation of thermally responsive material as the latter expands andcontracts volumetrically. The end of cylinder 94 adjacent enlargedportion 96 is closed by a plug 100 in the same manner as that describedwith respect to plug 74 in the embodiment of FIG. 3. The embodiment ofFIG. 4, if desired, may also include a heat-conducting shank integralwith or otherwise fixedly carried by plug 100 similar to shank 76 of theembodiment of FIG. 3. Referring now to FIG. 4, plug 100 may be providedwith a shank 99 formed integrally therewith or otherwise fixedly securedthereto. Shank 99, like plug 100, is formed of a material having ahigher thermal conductivity than that of the thermally responsivematerial 98, through and against which the shank 99 extends in good heattransfer relation. As with the embodiment shown in FIG. 3, piston 88 isprovided with a bore 97 for the reception of the distal end of shank 99.The co-operation of shank 99 with plug 100 and bored cylinder 88'provides substantially all of the advantages provided by theirrespective counterparts in the FIG. 3 embodiment.

An advantage of the embodiment of FIG. 4 is the increased volume ofthermally responsive material per unit length of the cylinder of theactuator with the resulting increased amount of movement of the pistonper unit change in temperature of the thermally responsive material.

With the embodiment of FIG. 4 and so long as thermally responsivematerial 98 is in the form of a unitary piece, insertion of therespective parts into tubular member 94 would be accomplished from thelower end of the latter as viewed in FIG. 4, after which plug would besecured in place. When thermally responsive material 98 of the FIG. 4embodiment, as well as thermally responsive material 78 of the FIG. 3embodiment, are in particulate form, it would be possible and oftenpreferable to secure the respective plug in place before inserting thethermally responsive material and remaining parts from the upper oropposite end of the respective tubular or cylinder-providing member.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

Dimensions of certain of the parts as shown in the drawing have beenmodified for the purposes of clarity of illustration.

As many changes could be made in the above constructions withoutdeparting from the scope of the inven tion, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings, shall be interpreted as illustrative and not in a limitingsense.

I claim:

1. A thermally responsive actuator comprising a cylinder; a pistondisposed in said cylinder to provide a hollow chamber therewithin; asealing member secured to and sealing one end of said cylinder, saidchamber having disposed therewithin thermally responsive material havinga higher coefficient of thermal expansion than the material of saidcylinder and member; means urging said piston in a direction forpressure engagement with said material; said member including a rod-likemember projecting into said chamber toward said piston; said pistonbeing provided with a bore opening into said chamber for reception ofthe distal end of said rod-like member for reciprocal sliding movementtherewithin; said rod-like member being disposed in intimateheattransfer relationship with said cylinder, sealing member and saidthermally responsive material; and said cylinder, sealing member, androd-like member each being formed of material having a higher thermalconductivity than that of said thermally responsive material.

2. A thermally responsive actuator comprising a cylinder; a pistondisposed in said cylinder to provide a hollow chamber therewithin; asealing member secured to and sealing one end of said cylinder, saidchamber having disposed therewithin thermally responsive material havinga higher coefficient of thermal expansion than the material of saidcylinder and member, said thermally responsive material being solid andelastically deformable during operating temperatures at whichthermostatic response is desired; means urging said piston in adirection for pressure engagement with said material; said memberincluding a rod-like member projecting into said chamber toward saidpiston; said piston being provided with a bore opening into said chamberfor reception of the distal end of said rod-like member for reciprocalsliding movement therewithin; said rod-like member being disposed inintimate heat-transfer relationship with said cylinder, sealing memberand said thermally responsive material; said cylinder, sealing member,and rod-like member each being formed of material having a higherthermal conductivity than that of said thermally responsive material.

3. A thermally responsive actuator comprising a tubular member, saidtubular member including a cylindrical portion and a flared enlargeddiameter end portion adjacent said cylindrical portion; a pistondisposed in said cylindrical portion to provide a hollow chambertherewithin; a flat plate-like member secured to and sealing saidenlarged diameter end portion of said cylinder; said chamber havingdisposed therewithin, thermally responsive material having a highercoefficient of thermal expansion than the material of said tubularmember and platelike member; means urging said piston in a direction forpressure engagement with said material; said member including a rod-likemember projecting into said chamber toward said piston; said pistonbeing provided with a bore opening into said chamber for reception ofthe distal end of said rod-like member for reciprocal sliding movementtherewithin; said rod-like member being disposed in intitmateheat-transfer relationship with said tubular member, plate like member,and said thermally responsive material; said tubular member, plate-likemember, and rod-like member each being formed of material having ahigher 20 than the material of said tubular member and plate-likemember; said thermally responsive material being solid and elasticallydeformable during operating temperatures at which thermostatic responseis desired; means urging said piston in a direction for pressureengagement with said material; said member including a rod-like memberprojecting into said chamber toward said piston; said piston beingprovided with a bore opening into said chamber for reception of thedistal end of said rod-like member for reciprocal sliding movementtherewithin; said redlike member being disposed in intimateheat-transfer relationship with said tubular member, sealing member, andsaid thermally responsive material; said tubular member, plate-likemember, and rod-like member each being formed of material having ahigher thermal conductivity than that of said thermally responsivematerial.

References Cited in the file of this patent UNITED STATES PATENTS2,368,181 Vernet Jan. 30, 1945 2,534,497 Albright Dec. 19, 195012,548,941 Brown Apr. 17, 1951 2,736,604 Albright Feb. 28, 1956 252,815,642 Sherwood Dec. 10, 1957 OTHER REFERENCES Silastic Facts, No. 8,Silastic 152 by Dow Corning Corp, Midland, Michigan, March 1952.

Summary of Silastic Stocks and Pastes, by Dow Corning Corp, Midland,Michigan, June 1958.

